30mph top speed!!! :-(

Okay so heres the story... Early today I noticed the jeep being really sluggish. I sorta ignored it because thats usually what i do(bad habit) until something goes reallly wrong. Well anyway after driving maybe 30 min more i notice a very BIG drop in power. Under normal acceleration and driving up hills it would peak at 2000-2500 rpm. If i were in a gear and i start to loose speed, i would downshift but floored it would only make 2500 rpm and the engine would make a groaning sound. The jeep idles smooth but even if you try and rev it it only peaks at 3000 floored and it slowly starts to drop off to 2500.
I've searched around an read similar stories and theres a whole variety of things: sensors, ignition, fuel, and exhaust.
I think its a clogged cat and or o2 sensor. The reason i've come to this conclusion is because i replaced most all my ignition components last year along with my fuel pump and filter. Ever since i bought the xj the cat has had a slight rattle. Around a week ago the slight rattle turned into the loudest most annoying rattle ever. Sometime last week I got a check engine light from my o2 sensor reading high. My friend says its my TPS another says its IAF. I think my cat fell apart inside thats why its clunking around bad and maybe why my o2 sensor set of the CEL. If you hit the cat on the bottom with a hammer slightly something inside bounces around like a rock?
Sorry for sounding pretty dumb but its all guesses for me. I'm just looking for any input from anyone who might have more knowledge or experience.

Btw its a 98 4.0 ax15
Thanks in advance!

Sounds like you are on it with the cat and the o2sensor, have fun.

cat conv.

change your o2 sensors while your at it.

pete

Could be a blown head gasket, the symptoms you describe are exactly what happened to a guy I know, (can’t call him a friend, cause I can’t stand him…but that’s another story)
This is easy to diagnose
Check the coolant for low level or oil and check the oil for milky contamination.
If any of that is evident…then theirs yer problem.
One more check to be sure would be a compression test, if two cylinders next to each other have lower compression, your head gasket is suspect.

Definately sounds like a plugged cat.

Quick check is to unbolt it @ the flange (2 bolt/nuts and 2 stud/nuts), and run it. If it revs fine, replace cat and/or muffler.

Jeff

Clogged cat, or 1/2 of it is now in your muffler, creating a cork in the system (don't ask! I was fired because mine made me late!)

Check all your sensors as well if u can. TPS, IAC, MAP and grounds and plugs/wires too for the heck of it.